"Power corrupts; absolute power corrupts absolutely." We're sure you've heard the saying, attributed to English historian Lord Acton, before, and chances are, you've seen it firsthand in a friend who is a bit less friendly after getting a bit of fame or power. But why is that?

Neuroscientist Sukhvinder Obhi and his colleagues at Wilfrid Laurier University in Ontario, Canada, may have the answer: power fundamentally changes a person's brain. In their study, published in the Journal of Experimental Psychology, the researchers put participants in the mindset of either being powerful or powerless, then they monitored the mirror system, the part of their brains linked with empathy.

It turns out, feeling powerless boosted the mirror system — people empathized highly. But, Obhi says, "when people were feeling powerful, the signal wasn't very high at all."

So when people felt power, they really did have more trouble getting inside another person's head.

"What we're finding is power diminishes all varieties of empathy," says Dacher Keltner, a social psychologist at University of California, Berkeley ...